lecture 27

Question 1

what were the first organisms on the earth and how long have they been here

Answer 1

the first were bacteria, they first developed on earth 3.8 billion years ago

Question 2

describe the bacterial genome

Answer 2

typically a single circular genome that is not contained within a nuclear envelope

Question 3

whats a nucleoid

Answer 3

nucleoid is the region of the cytoplasm that the genome of the bacteria is suspended in

Question 4

what are plasmids

Answer 4

other genomic sequences that are free in the cytoplasm and are separate from the whole genome.

Question 5

about how many genes are contained in the bacterial genome

Answer 5

about 500

Question 6

why does the small genome support the idea they were on earth first

Answer 6

as their genome is much shorter and more specialised. so they have evolved to produce less unnecessary DNA

Question 7

what do archaea and bacteria not have

Answer 7

membrane-bound organelles or a nuclear envelope

Question 8

what are the functions of the bacterial cell wall

Answer 8

its a macromolecule layer that provides strength to the cell
and it protects the cell against lysing and confers the cell shape

Question 9

what are mycoplasmas

Answer 9

prokaryotes that lack a cell wall, they are a group of pathogenic bacteria

Question 10

whats the main component of the bacterial cell wall

Answer 10

peptidoglycan

Question 11

whats the structure of the peptidoglycan fibres

Answer 11

a chain of NAM and NAG molecules

Question 12

what does tetrapeptide do

Answer 12

it vertically links the peptidoglycan chains

Question 13

what peptidoglycan component is the tetrapeptide on

Answer 13

its on the NAM molecule

Question 14

what are the peptidoglycan chains joined by

Answer 14

they are joined via amino acid cross bridges which links to the tetrapeptides

Question 15

what enzyme catalyses the cross linking of the tetrapeptides

Answer 15

this is transpeptidase

Question 16

what enzyme does penicillin target

Answer 16

the transpeptidase

Question 17

what does penicillin do?

Answer 17

blocks the transpeptidase, so the cross-linking of the cell wall doesnt occur, so when in liquid media the cells lyse and die

Question 18

what do the gram stains mean

Answer 18

gram stain blue is positive for peptidoglycan in the cells wall. gram stain pink is negative for peptidoglycan.

Question 19

describe gram stain process

Answer 19

Firstly crystal violet is added to sample. Then iodine is added, which acts as a mordant, fixing the stain to the cell wall. You then add alcohol to wash away the crystal violet. Then apply safranin, counterstain, see what colour the thing goes.

Question 20

how thick is the cell wall of peptidoglycan if present

Answer 20

20-80nm

Question 21

why is positive blue

Answer 21

because the initial crystal violet is absorbed by peptidoglycan layers and doesn;t get washed by the alcohol

Question 22

describe structure of gram positive cells

Answer 22

they have a thick layer of peptidoglycan on the outside of their cell membrane

Question 23

structure of gram negative cells

Answer 23

they have a thin layer of peptidoglycan, 5-10nm between the plasma membrane and an outer membrane.

Question 24

what does flagella do

Answer 24

The flagellum rotates, this rotation allows the bacteria to move in liquid media

Question 25

what are the flagella made of

Answer 25

These flagella are made of proteins and are rather small, having a 10-20 nm diameter.

Question 26

what are the three components of the flagella, describe them

Answer 26

There are 3 major functions of the flagella:
Long filament: extends into the medium which the cell is suspended in, this part is composed of subnits of flagellin protein
Hook: curved section connecting the long filament to the cell surface
Basal body: anchors the flagellum into the cell membrane by plates

Question 27

the bacterial cells do what movement type, and whats different to other things in this taxis

Answer 27

chemotaxis, they are too small to notice spactial gradients, instead they use temporal gradients.

Question 28

what are fimbriae

Answer 28

Function: Structures with adhesive properties that
cause bacteria to stick/adhere to surfaces, Much shorter and more numerous than flagella “hairlike”, 100-1000/cell and 2-8 nm in diameter. 1 µM in
length

Question 29

do all cells have fimrbiae and how do they help the bacteria

Answer 29

Not all bacteria posses these, it is more an inherited trait as they are passsed on from parent cells when its need.
These have receptors to tell what environment they are colonising. so they are only present in bacteria which need to be present and stuck to specific area

Question 30

whats a special type of fimbriae

Answer 30

the sex pilus

Question 31

whats the sex fimbriae and whats it do

Answer 31

Massive protein structure, connecting two bacterial cells.
The connection of two cells ios a conjugative pilus.
They use this to trransfer DNA from one cell to another in a process called conjugation.
Conjugation is a form of horizontal gene transfer.

Question 32

whats glycocalyx

Answer 32

A gelatinous polysaccharide and or polypeptide covering the outer side of the cell.
This forms a sticky meshwork of fibres

Question 33

whats a capsule

Answer 33

An organised defined structure attached firmly to cell wall

Question 34

whats a slime layer

Answer 34

Glycocalyx disorganised without cell shape, attached loosely to cell wall

Question 35

capsules serve what purpose

Answer 35

Bacteria will capsule are hard to eradicate.
Capsules are Virulence factors- protecting bacteria from phagocytosis and being engulfed by immune cells.
Also prevent dessication

Question 36

why do bacteria form endospores and when

Answer 36

These are formed during unfavourable growth conditions. so too low nutrients and too high bacteria density. These protect cells from stress, only two types of bacteria do this

Question 37

endospores only form for what

Answer 37

gram postive cells

Question 38

whats a virulence factor

Answer 38

protecting bacteria
from phagocytosis and engulfment by
immune cells.